This invention relates to audio teleconferencing systems. These are systems in which three or more participants, each having a telephone connection, can participate in a multi-way discussion. The essential part of a teleconference system is called the conference “bridge”, and is where the audio signals from all the participants are combined. Conference bridges presently function by receiving audio from each of the participants, appropriately mixing the audio signals, and then distributing the mixed signal to each of the participants. All signal processing is concentrated in the bridge, and the result is monaural (that is, there is a single sound channel). This arrangement is shown in FIG. 1, which will be described in detail later. The principal drawback with such systems is that the audio quality is monophonic, generally poor, and it is very difficult to determine which participants are speaking at any one time, especially when the number of participants is large.
An example is given in European Patent Specification 0291470. This discloses an arrangement in which some of the input symbols are inverted in phase before combining them in the return channel thus allowing the cancellation, for each user, of his own voice.